1. Field of the Invention
This invention relates to elastomeric compression springs. The preferred embodiment of our invention is primarily directed to a novel compression spring formed from an hourglass-shaped preform that is orientated to provide a spring having substantial deflection over a predetermined operating range with minimal bulge outwardly. The invention has broad varied applications that may include use in the front suspension fork of a mountain bike or the suspension of an off-highway mining truck. Applications wherein a guiding device, such as a tube or guide rod, is employed or where it is necessary to remove tolerance differences in a pad stack without causing a preload are also foreseen.
2. Related Art
Present designs of mountain bikes and off-the-road bicycles employ front fork suspension systems formed of a microcellular urethane spring encapsulated within a cylindrical unit that is interconnected between the front fork of a bicycle and its frame. These designs present problems because such urethanes absorb moisture that affects their proper functioning, lack integrity and durability due to flaking, and have a spring rate that imposes the additional cost of a dampener upon the manufacturer.
Also related to this application are spring elements formed of the same material as the instant invention and whose molecular structure is oriented through a similar process. The first in a series of these spring element patents are in U.S. Pat. No. 4,198,037 and U.S. Pat. No. 4,566,678 to David G. Anderson and assigned to the assignee of the present application. The thermoplastic elastomer discussed in these references is a copolyester polymer elastomer such as sold by E. I. DuPont de Nemoirs of Wilmington, Del. under the Trademark "HYTREL.RTM.". Each of these patents focuses on a method of manufacture of compression springs from HYTREL material and its associated compression set problems. Both are primarily directed to applications requiring very high spring rate for absorbing substantial quantities of energy in applications such as in the railcar industry.